Recently electric vehicles have been receiving much attention from environmental perspectives. Such electric vehicles are provided with rotating electrical machines (motors) as a source of power and a smoothing transformer (reactor) in the inverter circuit. Consequently, those components are expected to have improved efficiency. For this reason, a magnetic core for the rotating electrical machine or smoothing transformer are required to have high resistivity and magnetic flux density.
The following patent documents 1 to 3 disclose technologies to achieve higher resistance in a magnetic core.
Japanese Patent Laid-open No. 2006-41203 and Japanese Patent Laid-open No. 2006-283042 disclose a compacted magnetic core with high resistance achieved by coating a surface of iron powder particles with a fluoride insulating film. In addition, Japanese Patent Laid-open No. 2006-97124 discloses a magnetic core with high resistance achieved by applying magnesium on surfaces of iron powder particles and heat-treating them to form MgO films.